Field of the Invention
This invention relates generally to the drilling of holes to a preselected depth, and more specifically to a drill which is utilized for drilling blind holes and which can be adjusted to provide the precise depth of drilling wherein the adjustment can be done externally of the tool and independent of the stroke of the mechanism doing the drilling.
There are many instances where controlled depth of drilling needs to be performed. One specific technology in which controlled depth drilling is required is in the drilling of blind holes in substrate material for the packaging of semi-conductor chips. In this particular technology, a multi-layer circuit board is provided having various levels of circuitry which require vias of different depths to connect with different levels of circuitry.
It has been conventional prior art practice to provide a series or gang of drills operated by a common arm to drill to the desired depth. The conventional practice for adjusting the depth is to provide a very rough adjustment of the depth by means of screwing the drills onto a support collar on a frame and then providing a fine or final adjustment of each drill by adjusting the depth of the socket in the spindle into which the drill bit is to be inserted. Conventionally a set screw or some other type of recessed screw is provided at the end of the socket. In this case, the drill must be completely removed from the set up and this depth screw changed and the drill reinserted to provide for the fine adjustment of the depth of drilling.
When a series of drills are used, there may be frequent requirements for fine adjustment due to various factors during the drilling operation which necessitates frequent down time with excessive delays in removing the specific drill involved, removing the drill bit and adjusting the socket and then reassembling the drill into the rig during which time all drilling is suspended. Thus, it has become desirable to provide a drill which can be very quickly and easily fine adjusted externally without dismantling the drill from its support frame to provide final and precise adjustment of the depth to which drilling takes place.
There have been many prior art devices which in various manners provide for adjustment of depth of drilling. These include U.S. Pat. Nos. 4,619,564 4,557,646; 4,592,257; 4,115,017; 4,436,462; 3,911,542; 3,677,560; 3,460,408; 3,400,616; 2,908,978; 2,710,549; 2,402,353; 2,359,859; 2,301,151; 3,347,115; 3,844,672; and 3,178,969. While these patents show various techniques for adjusting the depth of drilling, nevertheless none of them teaches or suggests the specific structure wherein an external adjustment can be quickly made on a drill bit without removing it from the rig and the depth adjusted irrespective of the length of the stroke of the actuating structure.